Television receiver



Sept. 19, 1944. w. A. ToLsoN TELEVISION RECEIVER 2 Shets-Sheet 1 Filed July 31, 1941 5 a a fi/ M W L a v Z/IJ m2 5 M y 1 a y p /l Z n. K wp M a a aw. a m g 4 m i k0 w r c Mmw Wm 0 WNW GEM 2 m3. Q s r 1 J a Sept. 19, 1944.

W. A. TOLSON TELEVIS ION RECEIVER Filed July 31, 1941 2 Sheets-Sheet 2 -56, I l I W .odmf. 1 57 Patented Sept. 19, 1944 TELEVISION nncinvmt William A. Tolson, Westmont, N. .1., assignor to Radio Corporation of America, a corporation of Delaware Application July 3'1, 1941,s ria1No.4o4,'zs6

11 Claims.

triggered oif by an incoming-synchronizing pulse,

there may be a change in the latter portion of the pulse (due to noise, for example) which will affect the oscillator output.

An object of the present invention is to pro-'- vide an improved method of and means for synchronizing a cathode ray deflecting circuit;

A further object of the invention is to provide an improved deflecting circuit for use in a television receiver employing interlaced scanning.

A still further object of the invention is to provide an improved deflecting circuitwhichis little affected by undesired variations in the synchronizing signal.

In a preferred embodiment of the invention,

the vertical deflecting circuit of a television receiver contains a blocking oscillator whichis synchronized by vertical synchronizing pulses applied through an amplifier tube. The coupling circuit between the amplifier tube and the oscii- 'lator is such that the oscillator pulse, which occurs as soon as the oscillator is triggered ofiby the first occurring portion of a synchronizing pulse, drives the plate of the amplifier tube negative and holds it negative during the remainder of the synchronizing pulse. Thus, any variations in the latter portion of the synchronizing pulse cannot affect the oscillator output.

The invention will be better understood from the following description taken in connection with the accompanying drawings in which Figure 1 is a circuit and blockdiagram of a television receiver which includes one embodiment of my invention, W q

Figures 2a and 2b are curves which are referred to in explaining the invention, and I Figures 3, 4 and 5 are circuit diagrams of other embodiments of the invention. 1

In the several figures corresponding parts are indicated by like reference characters.

Referring to Fig. 1, the invention is shown applied to a television receiver which is to operate ina system employing odd-line interlacing, the synchronizing signal being the standard signal illustrated in Bedford Patent 2,223,812 issued December 3, 1940. The receiver is of the usual superheterodyne type'having a first detector and tunable oscillator indicated at l'fl. an I. F. amplifier III, a: second detector l2, a video amplifier l3, and a cathode ray receiver tube I4.

5: The tube I4 is provided withv horizontal deflecting coils I6 and vertical deflecting coils l1.

' Signal from J the second detector is supplied over a' conductor 18 and through an amplifier l9 toa separating tube 2|. In the particular cir-.

1o cuit illustrated, tl'ie'separating tube 2| is of the grid leak biased type, only the horizontal and vertical synchronizing pulses, which are positive at the grid ofthe tube 2|, appearing in its plate circuit.

=l 5 The horizontal or'line frequency synchronizing pulses, after being amplified and separated fromthe verticalsynchronizing pulses in a circuit'indicated at 22, are applied to the horizontal deflecting circuit indicated at 23.

20 The vertical synchronizing or framing pulses are-separated from the horizontal synchronizing pulses by a suitable filtering or integrating circuit as is well known in :the art. In the particular'circuit shown, the input circuit of an amplifier tube 24 includes an integrating circuit which comprises a series resistor 26 and a shunt condenser 21 connected :between the grid of tube 24and ground. A'small positive biasisapplied -to the grid of the tube 24 through a resistor 28 'and the resistor. 'Thisspecific integrating circuit is described and claimed in Patent 2,219,- -579 issued October .29, 1940 to W. J. Poch.

The resistor 29 and condenser 3| are the usual plate resistor and coupling condenser, respectively.

The vertical synchronizing pulse at the grid of the amplifier tube 24 has a'wave shape substantially as shown by the'curve 32 in Fig. 2a. This pulse is amplified by the tube 24 and applied to a blocking oscillator 33 which is adjusted in the usual manner to have a free-running frequency "slightly lower than the synchronous frequency. .The blocking oscillator 33 comprises a vacuum tube 34 and the usualiron-co're feedback transformer 36, grid condenser31- and grid leak resistor-38. The oscillator'pulses are applied to a suitable saw-tooth wave generating circuit which, 'in'this example, comprises a discharge tube 39 through which a condenser 4| isdischarged rapidly after beingcharged comparatively slowly through a plate resistor 42. The conventional fpeaking resistor 43 may be employed so that the output tube 4 will produce deflecting current in the coils 11 which has a straight saw- -tooth-wave form function.

46 and a plate resistor 41. The condenser (Bis: 1

The plate of tube 24 is connected to one end p of the secondary of the feed-back transformer 36, and through this secondary and; thegrid;

the usual filter condenser.

condenser 31 to the grid of the oscillator tube 34.

A condenser 5| is connected-between-theplate ground, is connected to ground through the plate resistor 59 and the amplifier plate voltage supply,

In the several figures the values of various circuit elements have been indicated, merely by way of example, in ohms, megohms, microfarads, and micromicrofarads. V

I claim as my invention:

1. In combination, an oscillator which is to be synchrbnized by synchronizing pulses, said oscillater being of the type which produces periodic voltage pulses of highamplitude, an amplifier "tube through which said synchronizing pulses j'alare applied to said oscillator, said tube having of'tube 24 and ground, this condenser having the" effect of widening the oscillator pulse to produce the pulse 52 (Fig. 2b) which appears onsaid plate. I to widen the pulse 52 enough so that the plate of tube 24 is 'held negative .until, substantially the end of the synchronizing pulse132 .orlonger. This action of the circuit in disconnecting or rendering. nonconducting. the tube 24 is illustrated in. Fig. 2b. .It. is apparent that. the nega; tive pulse52producedby the oscillator makes the tube. 24:.inefiective to transfer signal assoon as the'synchronizing pulse; 32 rises to a voltage high enough to? trigger oif the: oscillator, and thatthe pulse 52 holds the tube 24 in this. condition long enough to prevent the remainder otthesynchronizing pulse 32 from afiecting the osoillator.,,,

.It will be understood thatthe valuesoi circuit elements and of tube voltages are not critical. However, they must be such thatfora substan- The capacity of condenser 5| is sufficient a cathode and a, plate, and means for coupling thefplate of} said amplifier to a point in said 'oscillator' where negative oscillator pulses occur withsufficient amplitude to drive said plate negativewith'respect to said cathode immeditial period the oscillator voltagev 52. is. greater than the plate operating. voltage-cf. tube 24.. In the. circuit of Fig. 1 less than normal operating voltage is applied to. the plate of thetube 2,4 whereby less oscillator voltage is requiredatthe amplifier plate to hold it negative. .for-thereguired Figs. 3,v 4 and..5 show. othercircuitsfor connecting the amplifierllto the. oscillator; to obtain the. above-described operation.

In Fig.l.3 the plate of tube 24' is "eenneetiedtb the ratedQplate voltage through a plate resistor '53 of. unusually high resistance. As .in Fig.. 1,

there isa condenser, indicated at, 54, connected .between the amplifier plate. and ground. ,The

oscillator grid. condenser56 has a fa rly; small capacity whereby a .very steepfront for the oscillator pulse. 52'. is assur.ed;.-. The -.rel ativ e values of elements 53 and 5.4 are such that they widen. the

oscillator pulse a sufiicient amount to holdjnbc 24, nonconducting for therequiredtime as explained in connectionwith Fig.1. It ,m ay..be .noted that this widening of the oscillator'pulse the'pulse 52 (Fig. 2b); and performsthe same The .oscillaton'grid leak reSiSbQrJJ is connectedfrom the junction point of I the. condenser 58 and the transformer; secondary to round. InFig. 5, also, the oscillator voltage'across the grid circuit condenser 51 is utilized to drive the plate of tube 2 l negative. Here@t h e grid leak resistor 6|, instead of being connecteddirectlyto ately following the occurrence of a synchronizing pulseand to hold it negative at least for substantial y th dura n o 1 h n ronizin pu se-.1. 2. The invention according to claim l wherein said coupling means includes means for increasinathenrifih. o theaos i lat pu s- 3. Theinvent ohaoco d h ac m 1 w e ein thereis .acondenser connected between the plate of said..am'p1ifie a d rou d for wide in th il a or pu ses. 1 1 1 Y e1. Incombinatioaa blockin sc ato wh h is. .to be. synch onized y. synchr n p n amplifier tube, t o hwhi h. i pu e are applied to said oscillator, said tube having a plate, and me n .for ou l n th plate 01 i mp ifier, toapoint in said. s i' l toliwhere ne ative oscill torjp l e cur with sufiicient amplitude to drive saidplate negative with respect to. th cat ode. mm diately lowin ;th o currence. o a syn ro izi puls and to holdit .negative'at least for. substantially .the duration of ;.the synchronizingpulse g :5. The-inventionaccording to claim! wherein said coupling means in'cludes;, rnea;1s., tonincreasing thewidth of. the oscillator1pulses.;j. ...6,.'I'h.e.inveh ion..according to claime. wherein.-t here is; a cond n ersco n cted between. the plate; oiqsaid, amplifier. and groundi'orrwidenng the. oscillatorpulsea- 6 In combination, ablocking ,osoillatorwhich isto: be synchronizedby a signal comprising. periodicpulses, an amplifier tube through which saidsighal i applied to .saidoscillator, said tube having-.812 Plate and acathodetand meansefor coupli -the. plate of. said am liflerto a point .in said; oscillator where. there; is. produced in response to. the application of; J a; synchronizing pulse an oscillator; Pulse; which drivessaid plate to a iDQtential. which .doe'snot .substantiallyexceed. the. potential of said cathodezand which holdsitnegative at leastliorgsnbstantially the duration. oLthaSYnchronizing pulse. .1 1 I 8..--'I'he invention.accordingtojclaim 7 wherein said \coupling means includes-:means for increasing. the .width. of the oscillator pulses. 9. The. invention according. to claim .7, wherein there. is a condenserconnected: betweenthaplate of said amplifier.a .'d:.'g Q nd ;'f.or:.widening the .o i let pu sea,

10. Inpcomb nati n,

:blocking Jennie.

-ada ted t have its ratelot:osclllationcontrolled b the a pl cati n the eto off-a: frequency .contr llin si na m ans. i017 producing a frequency co t o lin sig a n:;whi:ch.there are periodical- .11? recurr n pulses; that .irecur: at a rate having a defini e ir m encrre a ion to saidra 1 oscillation, said oscillator comprising a vacuum tube having a control grid and a plate, said oscillator further comprising a transformer having a primary coil in the plate circuit of said tube and having a secondary coil in the grid circuit of said tube, one end of the secondary coil having a connection to said control grid, an amlplifier tube through which said controlling signal is applied to said oscillator, said amplifier tube having a plate, and means for coupling the plate 10 of said amplifier to a point in said oscillator where negative oscillatorpulses occur with sufllcient amplitude to drive the plate of said amplifier tube negative immediately following the occurrence of each of said pulses in the controlled signal and to hold it negative at least for substantially the duration of the pulses in the controlling signal, said coupling means including a connection from the plate of said amplifier to the other end of said secondary coil.

11. In combination, a blocking oscillator which is to be synchronized by synchronizing pulses,

said oscillator comprising a vacuum tube having a control grid and a plate, said oscillator further comprising a transformer having a primary coil in the plate circuit of said tube and having a secondary coil in the grid circuit of said tube, one end of the secondary coil having a connection to said control grid, an amplifier tube through which said synchronizing pulses are applied to said oscillator, said amplifier tube having a plate, and means for coupling the plate of said amplifier to a point in said oscillator where negative oscillator pulses occur with sufficient amplitude to drive the plate of said amplifler tube negative immediately following the occurrence of a synchronizing pulse and to hold it negative at least for substantially the duration of the synchronizing pulse, said coupling means including a connection from the plate of said amplifier tube to the other end of said sec- 20 ondary coil.

WILLIAM A. TOLSON. 

